Over the past five years, our Party has rallied the people and led them in solving a great number of problems that had long gone unsolved, securing many accomplishments that hold major future significance, and achieving i ________ advances in the cause of the Party and the country.

根据句意，本题需要填入一个形容词修饰“advances”，表示“在党和国家事业中取得的显著进展”。结合上下文，前文提到“解决了许多长期未解的问题”“取得许多具有重大未来意义的成就”，此处应填入“historic”（历史性的）或“historic”（历史性的）。 完整句子为： “Over the past five years, our Party has rallied the people and led them in solving a great number of problems that had long gone unsolved, securing many accomplishments that hold major future significance, and achieving **historic** advances in the cause of the Party and the country.” 答案：historic